I. Field
The present disclosure relates generally to communication, and more specifically to techniques for scanning for a wireless local area network (WLAN).
II. Background
WLANs are widely deployed to support wireless communication for terminals, which may be computers, cellular phones, and so on. WLANs are deployed in various locations such as office buildings, coffee shops, malls, airport terminals, and other hot spots where data usage is expected to be high. WLANs allow terminals to obtain data connectivity (e.g., to the Internet) from virtually anywhere in the world.
Many WLANs implement IEEE 802.11, which is a family of standards promulgated by The Institute of Electrical and Electronics Engineers (IEEE). The IEEE 802.11 standards specify the radio interface between access points and terminals and between terminals. Currently, 802.11a, 802.11b and 802.11g standards are widely used. Each IEEE 802.11 standard specifies operation at a specific frequency band (e.g., 2.4 GHz or 5 GHz) using one or more modulation techniques. In the following description, the WLANs are assumed to implement IEEE 802.11.
A terminal may be configured to search for a WLAN whenever the terminal is powered on. This search may be achieved by performing an active scan or a passive scan. For an active scan, the terminal transmits a probe request and waits for a probe response to detect the presence of a WLAN. For a passive scan, the terminal searches for a beacon transmitted by an access point in a WLAN. A beacon is a known transmission that contains pertinent information for a WLAN. An active scan typically consumes less battery power but requires the terminal to have regulatory information so that a probe request can be transmitted in accordance with regulatory requirements. Different countries may impose different regulatory requirements on the range of frequencies on which a WLAN can operate as well as the transmit power level for the terminals. A passive scan typically consumes more battery power but does not require regulatory information. In order to comply with the regulatory requirements for all countries, 802.11d requires the terminal to perform a passive scan first if it does not know the country in which it is located.
It is desirable to discover a WLAN with as little battery power as possible. There is therefore a need in the art for techniques to efficiently search for a WLAN.